mlxsw: spectrum_ptp: Increase parsing depth when PTP is enabled

Spectrum systems have a configurable limit on how far into the packet they
parse. By default, the limit is 96 bytes.

An IPv6 PTP packet is layered as Ethernet/IPv6/UDP (14+40+8 bytes), and
sequence ID of a PTP event is only available 32 bytes into payload, for a
total of 94 bytes. When an additional 802.1q header is present as
well (such as when ptp4l is running on a VLAN port), the parsing limit is
exceeded. Such packets are not recognized as PTP, and are not timestamped.

Therefore generalize the current VXLAN-specific parsing depth setting to
allow reference-counted requests from other modules as well. Keep it in the
VXLAN module, because the MPRS register also configures UDP destination
port number used for VXLAN, and is thus closely tied to the VXLAN code
anyway.

Then invoke the new interfaces from both VXLAN (in obvious places), as well
as from PTP code, when the (global) timestamping configuration changes from
disabled to enabled or vice versa.

Fixes: 87486427 ("mlxsw: spectrum: PTP: Support SIOCGHWTSTAMP, SIOCSHWTSTAMP ioctls")
Signed-off-by: Petr Machata <petrm@mellanox.com>
Reviewed-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>